This application pertains to the art of video inspection, and more particularly to specialized illumination and image capture therefor. The invention is directed to inspection of discrete specimens, particularly those having regions of heightened interest to the user. Accordingly, the application will be described with specific reference thereto, although it will be appreciated that the invention has broader application in any video inspection environment for which acquisition of detailed images is desirable.
High-speed, automated inspection of mass-produced articles is rapidly becoming an essential part of industrial production. As increasing reliance is placed on automated video inspection, increasing capability and resolution is also desired.
A first generation of improvement to the video inspection system was associated with improvements to basic inspection algorithms. A subsequent generation of improvement was directed toward improving the actual image captured. Such systems employed such components as a solid-state LED array, optionally coupled with a diffuser, to obtain more homogeneous lighting. Of course, the more uniform an illumination field, the more accurate a resultant, captured image would be.
An existing concern with state-of-the-art video inspection systems is competing objectives of analysis. More particularly, an overall analysis of an image is often desirable. However, detailed analysis of a sub-portion, or region, of the specimen or object is also advantageous. This latter advantage is particularly necessary for specimens having a high stress area or the like.
The need to provide a detailed analysis of a sub-portion of the image while maintaining global inspection of the inspected object can, in some instances, manifest itself as a critical machine vision inspection limitation. The limitations of current state-of-the-art machine vision systems become particularly apparent when a detailed inspection of a thin annular region located away from the object center is required. This situation often arises within the container industry wherein a fairly thin annular region located away from an object center is dedicated as a sealing surface for multi-piece containers. Product failure often occurs when this seal surface is compromised during construction of the container. For this reason, detailed inspection of this critical area of the object is a quality control requirement. However, the spatially-distributed nature of this critical area of interest does not lend itself to a detailed yet efficient machine vision inspection using state-of-the-art techniques. To obtain sufficient spatial resolution to discern defects of interest, several camera/imaging lens assemblies can be targeted along the annular region of interest, each focused to produce a magnified image of a unique portion of the object under inspection. In this fashion, a detailed analysis of the complete object can be synthesized. However, the requirement for multiple imaging lens/camera assemblies significantly impacts the cost of the machine vision solution. When a more economical single imaging lens/camera solution is pursued, detailed spatial resolution of the critical seal surface is sacrificed.
In short, the combination of standard imaging lens components and a generally rectangular array of sensor pixels does not efficiently sample thin annular regions which happen to be located away from the center of the object under inspection. When limited to using this inspection technique, the majority of the sensor pixels end up sampling non-critical regions of the part. Only a limited number of pixels are used to inspect the critical area of interest. This results in limited inspection resolution where it is required.
The subject invention addresses the above concerns as well as others and provides an efficient mechanism for completing detailed video inspection on limited annular regions of generally circular objects using a single imaging lens/camera assembly video inspection system.